I suggest Seeed...

Optional 3.3V jumper for MCP2515 on CAN-BUS Shield

Just hate ruining a nicely designed and brand new board like this to use 3.3V on the MCP2515. I can understand the design as the Uno is based on 5V logic and is also a requirement for the MCP2551 but for added compatibility it would be nice to see in future revisions.